1. Field of the Invention
The invention relates generally to the field of wellbore drilling systems and equipment. More specifically, the invention relates to electric power generators used with wellbore drilling equipment.
2. Background Art
Wellbore-deployed equipment includes various devices coupled in a conduit called a “drill string” suspended in a wellbore for the drilling of such wellbore. A drill string is a length of pipe generally assembled from segments (“joints”) threadedly coupled end to end and having a drill bit at the lower end of the drill string. Drilling is performed by rotating and axially urging the drill bit to the bottom of the wellbore to extend the length of the wellbore.
The foregoing devices can include measurement while drilling (“MWD”) and logging while drilling (“LWD”) instruments. Such instruments are typically disposed inside one or more pipe segments called “drill collars” and are threadedly coupled within the drill string proximate the lower end thereof MWD instruments generally include sensors for determining the geodetic trajectory of the wellbore so that adjustments to the trajectory may be made during drilling. LWD instruments include various sensors for measuring one or more petrophysical characteristics of the Earth formations surrounding the wellbore, such that the wellbore operator may evaluate the presence of useful materials in the formations, such as petroleum. Some types of MWD and/or LWD instruments include a telemetry device that modulates flow of drilling fluid (“mud”) through the drill string so that signals corresponding to certain of the measurements made by the various MWD and/or LWD instruments are communicated to the Earth's surface for decoding and interpretation while drilling operations are underway.
Irrespective of the types of sensors used in the MWD and/or LWD instruments with any particular drill string, it is necessary to supply electrical power to operate the sensors. Various devices used to supply electrical power for MWD and LWD instruments include batteries and turbine-operated electric generators. Each of the foregoing electrical power supplying devices is well known and widely used in MWD and LWD device operation.
Each of the foregoing electric power supplying devices has its own particular limitations. As a result, various devices have been conceived to attempt to use energy otherwise available in a wellbore to generate electrical power. U.S. Pat. No. 6,768,214 issued to Schultz et al. describes a power generator including a fluid conduit and a piezoelectric material attached to the conduit. When a pressure change takes place in the conduit, such as results from fluid flowing through the conduit, the piezoelectric material produces electricity due to flexing of the conduit. The conduit may include a reduced thickness portion, which has an increased degree of flexing in response to the fluid flow, with the piezoelectric material being attached to the reduced thickness portion.
U.S. Patent Application Publication No. 2006/0016606 filed by Tubel et al. describes a device, system, and methods of power generation in situ in a hydrocarbon producing well. A power generator for deployment in a hydrocarbon well tubular may comprise a housing adapted for deployment within a hydrocarbon well tubular; a mechanical to electrical power converter disposed at least partially within the housing, the mechanical to electrical power converter adapted to create an electric current when physically stressed; and a current converter operatively coupled to the mechanical to electrical power converter. Devices may be deployed downhole and operatively coupled to the power generator for their electrical power. Each of the foregoing devices uses energy in a flowing fluid in a hydrocarbon producing wellbore conduit to generate electrical power.
There continues to be a need for improved electrical power sources that can be used with wellbore drilling systems.